Engine lubricants for siloxane deposit control

ABSTRACT

A zinc free or substantially zinc free lubricant having a sulfated ash content of less than about 1.0 percent and including (a) an oil of lubricating viscosity; (b) 0.03 to about 3.0 weight percent of a phosphite compound; (c) an metal containing detergent; (d) a polyisobutylene succinimide dispersant derived from an ethylene polyamine and having a carbonyl to nitrogen ratio equal or greater than 1; (e) at least one other dispersant; (f) a boron containing compound in amount to provide at least 25 ppm boron to the lubricant composition is useful for inhibiting siloxane deposits in a stationary gas engine fueled by natural gas having a high silicon concentration.

BACKGROUND OF THE INVENTION

The disclosed technology relates to a lubricant for a sump-lubricatedinternal combustion engine, especially such an engine that is fueled bynatural gas, and more particularly, engines fueled by natural gassescontaining high levels of siloxanes and other silicon containingcompounds, such as are commonly found in landfill gases.

Internal combustion engines may be fueled by a variety of liquid orgaseous fuels, including natural gas. While liquefied natural gas orcompressed natural gas may sometimes be used to fuel small engines onvehicles, more typically natural gas is used to power large compressionignited or spark ignited “stationary gas” engines that may be fueled bynatural gas supplied directly from a gas wellhead. One commonapplication for stationary gas engines is at landfills, where theengines may be fueled by gas emanating from decomposition of refuse atthe landfill.

Landfill gasses tend not to be very clean and often have elevated levelsof silicon containing compounds and other corrosive materials. In anengine combusting landfill gas, the silicon containing compounds in thelandfill gas will form siloxane macromolecules which will deposit on theengine component surfaces leading to increased wear in the cylinders,valve areas and bearings. Over time, this wear reduces engineperformance, may cause valve seat recession, may increase oilconsumption, and may ultimately necessitate refurbishment of the engine.Typically, lubricants are replaced once the silicon concentration in thelubricant approaches 120 to 125 parts per million (ppm).

To prevent siloxane deposit buildup in engines operating on landfillgases (or other natural gas feedstocks containing high concentrations ofsilicon compounds), one existing method involves scrubbing the gasfeedstock through various filters and other media before using it as afuel stock for the engine. Scrubbing silicon compounds from landfillgases requires additional equipment that must be maintained andgenerally complicates the feed stream. Alternatively, lubricantformulations containing detergents and anti-wear agents have beenintroduced specifically for natural gas and landfill gas engines. Theselubricants are directed to cleaning the engine surface from siloxanedeposits and/or providing a sacrificial wear layer, but their efficacyis limited as detergency loses effectiveness and particularly once thesiloxane macromolecules have formed. Accordingly, these lubricantformulations require frequent replenishment/replacement leading toincreased lubricant consumption and engine downtime.

The present invention is directed to lubricant compositions which areformulated, according to the theory of the invention, to chemicallycleave siloxane macromolecules into smaller compounds that can be morereadily dispersed, thus reducing the formation of deposits and renderingthe silicon less detrimental in deposit formation even at lubricantsilicon concentrations of 125 ppm and higher. The subject lubricatingformulations may be effectively used in siloxane deposit control forlonger periods of time at elevated silicon concentrations, therebyfacilitating the use of unscrubbed natural and landfill gases andextending the oil change intervals, leading to less engine downtime.

Improved siloxane deposit control and extended cleanliness andperformance benefits may be provided by the lubricant of the disclosedtechnology.

SUMMARY OF THE INVENTION

The disclosed technology provides a method for lubricating asump-lubricated stationary gas engine, comprising supplying to theengine a substantially zinc-free lubricant comprising:

-   -   (a) an oil of lubricating viscosity;    -   (b) 0.03 to about 3.0 weigh percent with respect to the        lubricant composition (or 0.05 to 2.8 wt. % or 0.05 to 2.5 wt.        %) of a phosphite compound;    -   (c) a metal containing detergent;    -   (d) at least a first dispersant, wherein the first dispersant is        a polyisobutylene succinimide dispersant derived from an        ethylene polyamine and having a carbonyl to nitrogen ratio equal        or greater than 1 or 1:1 to 4:3 or 1.1:1 to 4:3;    -   (e) at least one other dispersant selected from the group        consisting of a succinimide dispersant having a carbonyl to        nitrogen ratio less than 1, a Mannich dispersant, and a        polyisobutylene succinic acid ester dispersant;    -   (f) boron containing compound in amount to provide at least 25        ppm boron to the lubricant composition;    -   wherein the lubricant composition is substantially free of zinc,        and    -   wherein the lubricant composition has a sulfated ash content of        less than about 1.0 wt. % (or 0.7 wt. %).

The disclosed technology further provides the lubricant as thusdescribed, and also provides a lubricant comprising:

-   -   (g) an oil of lubricating viscosity;    -   (b) 0.03 to about 3.0 weigh percent with respect to the        lubricant composition (or 0.05 to 2.8 wt. % or 0.05 to 2.5 wt.        %) of a phosphite compound;    -   an metal containing detergent;    -   (d) at least a first dispersant, wherein the first dispersant is        a polyisobutylene succinimide dispersant derived from an        ethylene polyamine and having a carbonyl to nitrogen ratio equal        or greater than 1 or 1:1 to 4:3 or 1.1:1 to 4:3;    -   at least one other dispersant selected from the group consisting        of a succinimide dispersant having a carbonyl to nitrogen ratio        less than 1, a Mannich dispersant, and a polyisobutylene        succinic acid ester dispersant;    -   (f) a boron containing compound in amount to provide at least 25        ppm boron to the lubricant composition;    -   wherein the lubricant composition is substantially free of zinc,        and    -   wherein the lubricant composition has a sulfated ash content of        less than about 1.0 wt. %.

DETAILED DESCRIPTION OF THE INVENTION

Various preferred features and embodiments will be described below byway of non-limiting illustration.

The amount of each chemical component described is presented exclusiveof any solvent or diluent oil, which may be customarily present in thecommercial material, that is, on an active chemical basis, unlessotherwise indicated. However, unless otherwise indicated, each chemicalor composition referred to herein should be interpreted as being acommercial grade material which may contain the isomers, by-products,derivatives, and other such materials that are normally understood to bepresent in the commercial grade.

Fuels

In the methods of the present invention, it is contemplated that thelubricant formulations will be employed in engines that are fueled withnatural gas and in some preferred embodiments, landfill gas. Landfillgas refers primarily to the source of the gas, namely, gas created bythe action of microorganisms within a landfill. Such landfill gas maycomprise only about 30 to 80 percent methane. In a particularly usefulembodiment, the method of operating the engine comprises operating theengine using as its primary or only fuel natural gas having aconcentration of silicon that is in excess of 10 mg/m³ or 15 mg/m³ or 20mg/m³ or 25 mg/m³ or 30 mg/m³ as measured by gas chromatography massspectrometry.

Base Oils

One element of the lubricating compositions of the present technology isan oil of lubricating viscosity. Such oils include natural and syntheticoils, oil derived from hydrocracking, hydrogenation, and hydrofinishing,unrefined, refined, re-refined oils or mixtures thereof. A more detaileddescription of unrefined, refined and re-refined oils is provided inInternational Publication WO2008/147704, paragraphs [0054] to [0056]. Amore detailed description of natural and synthetic lubricating oils isprovided in paragraphs [0058] to [0059] respectively of WO2008/147704.Synthetic oils may also be produced by Fischer-Tropsch reactions andtypically may be hydroisomerized Fischer-Tropsch hydrocarbons or waxes.In one embodiment oils may be prepared by a Fischer-Tropschgas-to-liquid synthetic procedure as well as other gas-to-liquid oils.

Oils of lubricating viscosity may also be selected from any of the baseoils in Groups I-V as specified in the American Petroleum Institute(API) Base Oil Interchangeability Guidelines. The five base oil groupsare as follows: Group I: >0.03% sulfur and/or <90% saturates andviscosity index 80 to 120; Group II: <0.03% S and ≥90% saturates and VI80 to 120; Group III: ≤0.03% S and ≥90% saturates and VI>120; Group IV:all polyalphaolefins; Group V: all others. Groups I, II and III aremineral oil base stocks.

The amount of the oil of lubricating viscosity present is typically thebalance remaining after subtracting from 100 wt % the sum of the amountof the compound of the invention and the other performance additives.

The lubricating composition may be in the form of a concentrate and/or afully formulated lubricant. If the lubricating composition of theinvention (comprising the additives disclosed hereinabove) is in theform of a concentrate which may be combined with additional oil to form,in whole or in part, a finished lubricant), the ratio of the of theseadditives to the oil of lubricating viscosity and/or to diluent oilinclude the ranges of 1:99 to 99:1 by weight, or 80:20 to 10:90 byweight.

Phosphite Antiwear Compounds

The lubricant compositions of the present invention will comprise atleast one phosphite compound. In some embodiments, the phosphitecompound will include at least one phosphite ester, and more usefully insome embodiments, at least one phosphite diester or triester compound.In one embodiment, the phosphite compound may comprise phosphorous acid(H₃PO₃).

It will be understood that the term phosphite includes the tautomer(s).Similarly it will be understood that phosphite esters may be referred togenerally as alkyl phosphites or alkyl hydrogen phosphites and theseterms may be used interchangeably.

Examples of suitable phosphite compounds may include compounds havingthe general Formula I

(R¹O)₃P   (I)

In the above formula, each le independently may be hydrogen or ahydrocarbyl group having 1 to 36, or 1 to 24, or 1 to 18 or 2 to 30 or 2to 24 or 2 to 10 carbon atoms or 12 to 36 or 12 to 30 or 12 to 20 carbonatoms. The hydrocarbyl group may be a linear or branched, may be asubstituted or unsubstituted, may be aromatic or aliphatic or alicylicor heterocyclic or may be saturated or unsaturated and each le may bethe same or different.

Exemplary phosphite monoesters may include phosphite monesterscomprising C₁ to C₃₀ hydrocarbyl groups.

Exemplary phosphite diesters may include dimethyl hydrogen phosphite,diethyl hydrogen phosphite, dipropyl hydrogen phosphite, dibutylhydrogen phosphite, diethylhexyl hydrogen phosphite, didecyl hydrogenphosphite, didodecyl hydrogen phosphite (dilauryl hydrogen phosphite),dioctadecyl hydrogen phosphite (distearyl hydrogen phosphite),di-9-octadecenyl hydrogen phosphite (dioleyl hydrogen phosphite),diphenyl hydrogen phosphite and the like.

Examples of the phosphite triesters include, for example, triphenylphosphite, triethyl phosphite, tributyl phosphite, tripropyl phosphite,trioctyl phosphite, tri-iso-octyl phosphite, tris 2-ethylhexylphosphite, tri-isodecyl phosphite, tris tridecyl phosphite, trioleylphosphite, etc. and the like.

In one embodiment, the phosphite ester may comprise a polyphosphiteester, which may be produced as the reaction product, e.g., condensationproduct, of a monomeric phosphorous acid or an ester thereof with atleast two alkylene diols. Exemplary polyphosphite esters are more fullydescribed in International Publication WO2016/089565.

In some embodiments, the phosphite compound may comprise a mixture oftwo or more phosphite compounds. In a particularly useful embodiment,the phosphite compound may comprise a first alkyl phosphite ester havingC2 to C10 hydrocarbyl groups and a second alkyl phosphite ester havingC12 to C30 hydrocarbyl groups. In one embodiment, the phosphite maycomprise a mixture of two or more phosphite diesters, wherein onediester has C2 to C10 hydrocarbyl groups and a second diester has C12 toC30 hydrocarbyl groups. In such an embodiment, the ratio of the C2 toC10 diester to the C12 to C30 diester may be from 20:80 to 80:20 or40:60 to 60:40 or 60:40 to 90:10. In still another embodiment, thephosphite may comprise dibutyl phosphite.

The phosphite compound may be present in the lubricating composition (onan oil free basis) in an amount from about 0.03 to about 3.0 weightpercent with respect to the lubricant composition (or 0.05 to 2.8 wt. %or 0.05 to 2.5 wt. % or 0.1 to 2.5 wt. % or 0.5 to 2.5 wt. % or 1.0 to2.5 wt. %).

In some embodiments, the phosphite compounds may be present in an amountto provide 0.001 wt. % to 0.05 wt. % phosphorus (or 10 to 500 ppmphosphorus), or 0.005 to 0.04 wt. % phosphorus, or 0.005 to about 0.03wt. % phosphorus to the lubricant composition. In still otherembodiments, the phosphite may contribute greater than 80% or 90% or 95%of the total phosphorous in the lubricant composition. In still anotherembodiment, the phosphite compound may constitute the only phosphorouscontaining antiwear additive in the lubricating composition. Thelubricant composition may be free of or substantially free of otherphosphorus containing antiwear compounds or other phosphorous containingcompounds. In some embodiments, the total amount of phosphorus in thelubricant composition may be less than about 0.03 wt. %

Dispersants

Another component in the lubricant compositions is a dispersant.Dispersants are well known in the field of lubricants and include whatare known as ashless-type dispersants and polymeric dispersants.Suitable dispersants may be chosen from a succinimide dispersant, aMannich dispersant, a succinamide dispersant, a polyolefin (typicallyisobutylene) succinic acid ester, ester-amide, or mixtures thereof. Thedispersant may be present as a single dispersant; however, a mixture ofmore than one type of dispersant is particularly useful. Metalcontaining (ash containing) dispersants may be used, but in someembodiments, the dispersant is free of or substantially free of ashcontaining dispersants.

Ashless type dispersants are characterized by a polar group attached toa relatively high molecular weight hydrocarbon chain. Typical ashlessdispersants include nitrogen-containing dispersants such asN-substituted long chain alkenyl succinimides, also known as succinimidedispersants.

The succinimide dispersant may be derived from an aliphatic amine,aliphatic polyamine, or mixtures thereof. The aliphatic polyamine mayinclude such compounds as ethylenepolyamine, a propylenepolyamine, abutylenepolyamine, or mixtures thereof. In one embodiment the aliphaticpolyamine may be ethylenepolyamine. In one embodiment the aliphaticpolyamine may be chosen from ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine,polyamine still bottoms, and mixtures thereof. Succinimide dispersantsare more fully described in U.S. Pat. Nos. 4,234,435 and 3,172,892.

In one embodiment, the dispersant may comprise the condensation productof a hydrocarbyl-substituted succinic anhydride or reactive equivalentthereof with an alkylene polyamine, wherein the alkylene polyamine is acondensed amine. Such dispersants derived from condensed amines are morefully described in U.S. Pat. Pub. 2009/0018040.

In one embodiment the succinimide dispersant may be a derivative of anaromatic amine, an aromatic polyamine, or mixtures thereof. The aromaticamine may be 4-aminodiphenylamine (ADPA) (also known asN-phenylphenylenediamine), derivatives of ADPA, a nitroaniline, anaminocarbazole, an amino-indazolinone, an aminopyrimidine,4-(4-nitrophenylazo)aniline, or combinations thereof. In one embodiment,the dispersant may comprise a derivative of an aromatic amine whereinthe aromatic amine has at least three non-continuous aromatic rings.

The succinimide dispersant may be a derivative of a polyether amine orpolyether polyamine. Typical polyether amine compounds contain at leastone ether unit and will be chain terminated with at least one aminemoiety. The polyetherpolyamines can be based on polymers derived fromC2-C6 epoxides such as ethylene oxide, propylene oxide, and butyleneoxide. Examples of polyether polyamines are sold under the Jeffamine®brand and are commercially available from Huntsman Corporation locatedin Houston, Tex.

Another class of ashless dispersant is high molecular weight esters,prepared by reaction of a hydrocarbyl acylating agent, such as asuccinic anhydride or alkylated (typically polyisobutylene) succinicanhydride or their reactive equivalents, and a polyhydric aliphaticalcohol such as ethylene glycol, propylene glycol, butylene glycol,pentaerythritol, mannitol, sorbitol, glycerol, diglycerol, triglycerol,tetraglycerol, erythritol, 2-hydroxymethyl-2-methyl-1,3 propanediol(trimethylolethane), 2-ethyl-2-(hydroxymethyl)-1,3 propanediol(trimethylolpropane), 1,3,4-hexane triol and mixtures thereof. Suchmaterials are described in more detail in U.S. Pat. No. 3,381,022.

A polyolefin succinic acid ester-amide may be a polyisobutylene succinicacid reacted with an alcohol (such as pentaerythritol) and an amine(such as a diamine, typically diethyleneamine).

Another class of ashless dispersant is Mannich bases. These arematerials which are formed by the condensation of a higher molecularweight, alkyl substituted phenol, an alkylene polyamine, and an aldehydesuch as formaldehyde and are described in more detail in U.S. Pat. No.3,634,515. Other dispersants include polymeric dispersant additives,which are generally hydrocarbon-based polymers which contain polarfunctionality to impart dispersancy characteristics to the polymer.

Where the dispersants described above are derived from a polyisobutylenesuccinic acid or anhydride, the polyisobutylene may have a numberaverage molecular weight of 350 to 5000, or 750 to 2500 or 500 to 1500or 750 to 1250.

A succinimide dispersant may be obtained/obtainable from achlorine-assisted process, often involving Diels-Alder chemistry,leading to formation of carbocyclic linkages from the hydrocarbon chainto the succinic moiety. The process is known to a person skilled in theart. The chlorine-assisted process may produce a dispersant that is apolyisobutylene succinimide having a carbocyclic ring present on 50 mole% or more, or 60 to 100 mole % of the non-borated dispersant molecules.Both the thermal and chlorine-assisted processes are described ingreater detail in U.S. Pat. No. 7,615,521, columns 4-5 and preparativeexamples A and B.

Alternatively, a succinimide dispersant may be prepared/obtained/obtainable from reaction of succinic anhydride by an “ene” or“thermal” reaction, by what is referred to as a “direct alkylationprocess.” The “ene” reaction mechanism and general reaction conditionsare summarized in “Maleic Anhydride”, pages, 147-149, Edited by B.C.Trivedi and B.C. Culbertson and Published by Plenum Press in 1982. Thedispersant prepared by a process that includes an “ene” reaction may bea polyisobutylene succinimide having a carbocyclic ring present of lessthan 50 mole %, or 0 to less than 30 mole %, or 0 to less than 20 mole%, or 0 mole % of the non-borated dispersant molecules. The “ene”reaction may have a reaction temperature of 180° C. to less than 300°C., or 200° C. to 250° C., or 200° C. to 220° C. The polyisobuteneparticularly useful in preparing an “ene” type succinimide dispersantmay desirably have at least 50 percent terminal vinylidene groups, suchas at least 60, or 70, or 80 percent.

In certain embodiments, the succinimide dispersant prepared by the“thermal” or “ene” route may be particularly useful.

The dispersants may also be post-treated by conventional methods by areaction with any of a variety of agents. Among these are boroncompounds (such as boric acid), urea, thiourea, dimercaptothiadiazoles,carbon disulphide, aldehydes, ketones, carboxylic acids such asterephthalic acid, hydrocarbon-substituted succinic anhydrides, maleicanhydride, nitriles, epoxides, and phosphorus compounds. In oneembodiment the post-treated dispersant may be borated. In one embodimentthe post-treated dispersant may be reacted with dimercaptothiadiazoles.In one embodiment the post-treated dispersant may be reacted withphosphoric or phosphorous acid. In one embodiment the post-treateddispersant may be reacted with terephthalic acid and boric acid (asdescribed in U.S. Patent Application US2009/0054278.

In one embodiment, the ashless dispersant may be boron-containing, i.e.,has incorporated boron and delivers said boron to the lubricantcomposition. The boron- containing dispersant may be present in anamount to deliver at least 25 ppm boron, or at least 50 ppm boron, or atleast 100 ppm or at least 200 ppm or 300ppm or 500 ppm or 200 to 500 ppmor 300 to 500 ppm boron to the lubricant composition. In one embodiment,the lubricant composition may be free of a boron- containing dispersant,i.e. the boron containing dispersant delivers no more than 10 ppm boronto the final formulation.

The lubricant compositions of the present invention include at least onepolyisobutylene succinimide dispersant derived from an ethylenepolyamine and having a carbonyl to nitrogen ratio equal to or greaterthan 1:1 or between about 1:1 to 4:3 or about 1.1:1 to 4:3 or about 1:1to about 6:5 or about 1.1:1 to about 6:5. This dispersant (on an oilfree basis) may be present in an amount of 0.1 wt % to 2 wt % (or 0.1 to1.5 wt %, or 0.2 wt % to 2 wt %, or 0.3 wt % to 1 wt %) of the lubricantcomposition.

The dispersant may typically comprise a dispersant package of two ormore dispersants. In one embodiment, the dispersant package comprises atleast one polyisobutylene succinimide dispersant derived from anethylene polyamine and having a carbonyl to nitrogen ratio equal to orgreater than 1:1 or between about 1:1 to 4:3 or about 1.1:1 to 4:3 orabout 1:1 to about 6:5 or about 1.1:1 to about 6:5 and a seconddispersant selected from dispersants having a carbonyl to nitrogen ratioless than 1:1 and succinic acid ester dispersants. In one embodiment,the second dispersant may be a conventional polyisobutylene succinimidedispersant. In another embodiment, the second dispersant may be apolyisobutylene succinic acid ester dispersant. The second dispersantmay by a Mannich dispersant. The second dispersant may be a borateddispersant.

In still a further embodiment, the dispersant package may comprise threeor more dispersants, including at least one polyisobutylene succinimidedispersant derived from an ethylene polyamine and having a carbonyl tonitrogen ratio equal to or greater than 1:1 or between about 1:1 to 4:3or about 1.1:1 to 4:3 or about 1:1 to about 6:5 or about 1.1:1 to about6:5, a second dispersant which is a polyisobutylene succinimidedispersant having a carbonyl to nitrogen ratio less than 1:1 and a thirddispersant which is an alkenyl (typically polyisobutylene) succinic acidester dispersant or a borated dispersant or a Mannich dispersant ormixtures thereof.

In a dispersant package comprising two or more dispersants, thepolyisobutylene succinimide dispersant derived from an ethylenepolyamine and having a carbonyl to nitrogen ratio equal to or greaterthan 1:1 or between about 1:1 to 4:3 or about 1.1:1 to 4:3 or about 1:1to about 6:5 or about 1.1:1 to about 6:5 will typically comprise fromabout 5 to 80 wt. % or 10 to 60 wt. %, 15 to 50 wt. % and 15 to 30 wt. %of the total dispersant package.

The total dispersant or dispersant package (on an oil free basis) may bepresent it the lubricant composition in an amount of 1.0 wt % to 6.0 wt.% or 1.5 wt. % to 5.0 wt. %, 2.0 to 4.0 wt. %.

Detergents

The disclosed lubricant may include one or more alkaline or alkali earthmetal-containing detergent. The metal-containing detergent which may bepresent as an additive component in the lubricant is, in one embodiment,an overbased detergent. It may, alternatively, be a neutral detergent.Overbased materials, otherwise referred to as overbased or superbasedsalts, are generally homogeneous Newtonian systems characterized by ametal content in excess of that which would be present forneutralization according to the stoichiometry of the metal and theparticular acidic organic compound reacted with the metal. The overbasedmaterials are prepared by reacting an acidic material (typically aninorganic acid or lower carboxylic acid, preferably carbon dioxide) witha mixture comprising an acidic organic compound (in this instance, ahydrocarbyl-substituted salicylic acid), a reaction medium comprising atleast one inert, organic solvent (e.g., mineral oil, naphtha, toluene,xylene) for said acidic organic material, a stoichiometric excess of ametal base, and a promoter such as a phenol or alcohol and optionallyammonia. The acidic organic material will normally have a sufficientnumber of carbon atoms, for instance, as a hydrocarbyl substituent, toprovide a reasonable degree of solubility in oil. The amount of excessmetal is commonly expressed in terms of metal ratio. The term “metalratio” is the ratio of the total equivalents of the metal to theequivalents of the acidic organic compound. A neutral metal salt has ametal ratio of one. A salt having 4.5 times as much metal as present ina normal salt will have metal excess of 3.5 equivalents, or a ratio of4.5.

Overbased detergents are often characterized by Total Base Number (TBN).TBN is the amount of strong acid needed to neutralize all of theoverbased material's basicity, expressed as potassium hydroxideequivalents (mg KOH per gram of sample). Since overbased detergents arecommonly provided in a form which contains a certain amount of diluentoil, for example, 40-50% oil, the actual TBN value for such a detergentwill depend on the amount of such diluent oil present, irrespective ofthe “inherent” basicity of the overbased material. For the purposes ofthe present invention, the TBN of an overbased detergent is to berecalculated to an oil-free basis. Detergents which are useful in thepresent invention typically have a TBN (oil-free basis) of 100 to 800,and in one embodiment 150 to 750, and in another, 400 to 700. Ifmultiple detergents are employed, the overall TBN of the detergentcomponent (that is, an average of all the specific detergents together)will typically be in the above ranges.

The metal compounds useful in making the basic metal salts are generallyany Group 1 or Group 2 metal compounds (CAS version of the PeriodicTable of the Elements). The Group 1 metals of the metal compound includeGroup 1a alkali metals such as sodium, potassium, and lithium, as wellas Group 1b metals such as copper. The Group 1 metals can be sodium,potassium, lithium and copper, and in one embodiment sodium orpotassium, and in another embodiment, sodium. The Group 2 metals of themetal base include the Group 2a alkaline earth metals such as magnesium,calcium, and barium, as well as the Group 2b metals such as zinc orcadmium. In one embodiment the Group 2 metals are magnesium, calcium,barium, or zinc, and in another embodiments magnesium or calcium. Incertain embodiments the metal is magnesium, calcium or sodium or amixture of calcium and magnesium. In some embodiments of the presentinvention, the lubricant is zinc free or substantially zinc free andthus will not include zinc containing detergents. Generally the metalcompounds are delivered as metal salts. The anionic portion of the saltcan be hydroxide, oxide, carbonate, borate, or nitrate.

In one embodiment the lubricants may contain an overbased sulfonatedetergent. Oil-soluble sulfonates can be represented by one of thefollowing formulas: R²-T-(SO₃)_(a) and R³-(SO₃-)_(b), where T is acyclic nucleus such as typically benzene; R² is an aliphatic group suchas alkyl, alkenyl, alkoxy, or alkoxyalkyl; (R²)-T typically contains atotal of at least 15 carbon atoms; and R³ is an aliphatic hydrocarbylgroup typically containing at least 15 carbon atoms. Examples of R³ arealkyl, alkenyl, alkoxyalkyl, and carboalkoxyalkyl groups. In oneembodiment the sulfonate detergent may be a predominantly linearalkylbenzenesulfonate detergent having a metal ratio of at least 8 asdescribed in paragraphs [0026] to [0037] of U.S. Patent Application2005-065045.

Another overbased material which can be present is an overbased phenatedetergent. The phenols useful in making phenate detergents can berepresented by the formula (R⁴)_(a)-Ar-(OH)_(b), wherein R⁵ is analiphatic hydrocarbyl group of 4 to 400 carbon atoms, or 6 to 80 or 6 to30 or 8 to 25 or 8 to 15 carbon atoms; Ar is an aromatic group (whichcan be a benzene group or another aromatic group such as naphthalene); aand b are independently numbers of at least one, the sum of a and bbeing in the range of two up to the number of displaceable hydrogens onthe aromatic nucleus or nuclei of Ar. In one embodiment, a and b areindependently numbers in the range of 1 to 4, or 1 to 2. R⁴ and a aretypically such that there is an average of at least 8 aliphatic carbonatoms provided by the R⁴ groups for each phenol compound. Phenatedetergents are also sometimes provided as sulfur-bridged species. Insome embodiments, the phenate detergent contains less than 20% or lessthan 10% or less than 5% or less than 2% or less than 1%, e.g., 0 or0.05% to 0.5% of monomeric para-dodecylphenol or sulfurized monomerthereof or salt thereof, based on the active chemical amount of thephenate detergent. Methods for preparing phenolic dispersants of thistype are disclosed in numerous applications or publications, includingPCT/US2012/060839, PCT/US2013/024877, and U.S. Pat. No. 7,435,709.

In one embodiment, detergent may comprise a salicylate detergent such asan overbased calcium hydrocarbyl-substituted salicylate detergent. Thepresence of a salicylate detergent may be beneficial in providingoxidation resistance to the lubricant. In one embodiment the salicylatedetergent has a Total Base Number of about 200 to about 700 or 250 to500 or 250 to 400 or 300 to 700 or 450 to 700 or greater than about 400on an oil free basis, that is, factoring out the effect of diluent oil.Salicylate detergents are known; see, for instance, U.S. Pat. Nos.5,688,751 or 4,627,928. In a particularly useful embodiment, thedetergent may comprise an overbased calcium salicylate detergent and inanother embodiment, an overbased magnesium salicylate detergent and instill another embodiment a mixture of calcium and magnesium salicylatedetergents.

In one embodiment, the overbased material is an overbased saligenindetergent. Overbased saligenin detergents are commonly overbasedmagnesium salts which are based on saligenin derivatives. Saligenindetergents are disclosed in greater detail in U.S. Pat. No. 6,310,009,with special reference to their methods of synthesis (Column 8 andExample 1) and suitable amounts of the various species of X and Y(Column 6).

Salixarate detergents may also be present. Salixarates and methods oftheir preparation are described in greater detail in U.S. Pat. No.6,200,936 and PCT Publication WO 01/56968. It is believed that thesalixarate derivatives have a predominantly linear, rather thanmacrocyclic, structure, although both structures are intended to beencompassed by the term “salixarate.”

Patents describing techniques for making basic salts of sulfonic acids,carboxylic acids, (hydrocarbyl-substituted) phenols, phosphonic acids,and mixtures of any two or more of these include U.S. Pat. Nos.2,501,731; 2,616,905;

2,616,911; 2,616,925; 2,777,874; 3,256,186; 3,384,585; 3,365,396;3,320,162; 3,318,809; 3,488,284; and 3,629,109.

Other overbased detergents can include overbased detergents having aMannich base structure, as disclosed in U.S. Pat. No. 6,569,818.

Either a single detergent or multiple additional detergents can bepresent. The amount of the detergent or detergents (individually or intotal) in the lubricants of the present technology may be 0.5 to 5percent by weight, or 1 to 3 percent. The amount in a concentrate willbe correspondingly higher. The total amount of detergents present in thelubricants of the disclosed technology may be an amount suitable toprovide 1 to 5 TBN, or 2 to 4, or 2.5 to 3 TBN to the lubricant.

Boron Compound

The lubricant compositions of the present invention may comprise a boroncontaining compound or mixture of boron containing compounds in anamount to provide the lubricant composition with 25 ppm boron, or atleast 50 ppm boron, or at least 100 ppm or at least 200 ppm or 300 ppmor 500 ppm or 200 to 500 ppm or 300 to 500 ppm boron to the lubricantcomposition. Useful boron containing compounds may include boric acid(including metaboric acid, HBO₂, orthoboric acid, H₃BO₃, and atetraboric acid, H₂B₄O₇) and borate esters, which may be prepared by thereaction of boric acid, a boric oxide, a boron trioxide or an alkylborate and at least one compound selected from epoxy compounds,halohydrin compounds, epihalohydrin compounds, alcohols and mixturesthereof. Typically the alcohols include monohydric alcohols, dihydricalcohols, trihydric alcohols or higher alcohols. Borate esters may alsobe prepared from boron halides.

The borated ester may contains at least one hydrocarbyl group oftencontaining about 4 to about 30, or 8 to about 30 carbon atoms.

In one embodiment, the boron containing compound may comprise a borateester comprising at least one C8 to C30 hydrocarbyl group. The boroncontaining compound may comprise one or more borated dispersantsdiscussed above. In one embodiment, it the boron containing compound maycomprise a mixture of a borate ester and a boron containing dispersant.

Other Performance Additives

The lubricant of the disclosed technology may also contain 3 to 80 ppm(or 5 to 70, or 10 to 60, or 20 to 50 ppm) of one or moresilicon-containing antifoam agents. At least a small amount of such anantifoam agent is desirable to minimize foaming while the lubricant islubricating the engine. However, an excessive amount may be deleteriousto the anti-emulsion performance of the lubricant as it may be used forthe lubrication of a compressor.

Silicon antifoam agents may be fluorinated molecules, or moleculeswithout fluorine, or mixtures of such molecules. Such materials arecommercially available and includes such species as polydimethylsiloxaneand trimethyl, trifluoropropylmethyl siloxane. These materials may beprovided commercially as oil-diluted compositions; the amounts reportedherein are an oil-free basis.

In certain embodiments, the disclosed lubricant may also contain asilicon-free polymeric antifoam agent. The amount of this agent, if itis present, may be up to 200 parts per million by weight, e.g., 10 to200, or 20 to 100, or 25 to 80, or 30 to 70 ppm. The silicon-freepolymeric antifoam agent may comprise an alkyl acrylate polymer, such asa copolymer of ethyl acrylate and 2-ethylhexyl acrylate. Such anantifoam agent may aid in improving anti-emulsion performance of thelubricant.

Another component that may be included in the lubricant is a corrosioninhibitor (which may also function as a rust inhibitor or a metaldeactivator). Corrosion inhibitors typically may includenitrogen-containing materials such as triazoles and thiadiazoles andderivatives thereof. Suitable triazoles include aromatic triazoles suchas benzotriazole or alkylbenzotriazoles such as tolutriazole.

Thiadiazoles include dimercaptothiadiazoles and mono- or di-alkylderivatives of dimercaptothiadiazoles.

(including species with multiple S atoms in a chain). The amount of thecorrosion inhibitor (such as the amount of the aromatic triazole) may be0.001 to 0.1 wt. %, or 0.003 to 0.03 wt. %, or 0.005 to 0.1 wt. %.

Additional conventional components may be used in preparing a lubricantaccording to the present technology, for instance, those additivestypically employed in a crankcase lubricant. Crankcase lubricants maytypically contain any or all of the following components hereinafterdescribed.

One component is an antioxidant, sometimes referred to an ashlessantioxidant if it is desired to distinguish metal-containing materialsfrom metal-free (ashless) compounds. Antioxidants encompass phenolicantioxidants, which may comprise a butyl substituted phenol containing 2or 3 t-butyl groups. The para position may also be occupied by ahydrocarbyl group or a group bridging two aromatic rings. They may alsocontain an ester group at the para position, for example, an antioxidantof the formula

wherein R³ is a hydrocarbyl group such as an alkyl group containing,e.g., 1 to 18 or 2 to 12 or 2 to 8 or 2 to 6 carbon atoms; and t-alkylcan be t-butyl. Such antioxidants are described in greater detail inU.S. Pat. No. 6,559,105. Antioxidants also include aromatic amines, suchas nonylated diphenylamines. Other antioxidants include sulfurizedolefins, titanium compounds, and molybdenum compounds. U.S. Pat. No.4,285,822, for instance, discloses lubricating oil compositionscontaining a molybdenum and sulfur containing composition. Typicalamounts of antioxidants will, of course, depend on the specificantioxidant and its individual effectiveness, but illustrative totalamounts can be 0.01 to 5 wt. % or 0.15 to 4.5 wt. % or 0.2 to 4 wt. %.Additionally, more than one antioxidant may be present, and certaincombinations of these can be synergistic in their combined overalleffect.

Viscosity improvers (also sometimes referred to as viscosity indeximprovers or viscosity modifiers) may be included in the disclosedcompositions. Viscosity improvers are usually polymers, includingpolyisobutenes, polymethacrylic acid esters, diene polymers,polyalkylstyrenes, esterified styrene-maleic anhydride copolymers,alkenylarene-conjugated diene copolymers and polyolefins.Multifunctional viscosity improvers, which also have dispersant and/orantioxidancy properties are known and may optionally be used. Viscosityimprovers may be used at, e.g., 0.1 to 0.8 wt. % or 0.3 to 0.6 wt. %.

The lubricant compositions of the present invention may include one ormore antiwear agents other than the phosphite compounds disclosed above.

Examples of other anti-wear agents may include phosphorus-containingantiwear/extreme pressure agents such as metal thiophosphates,phosphoric acid esters and salts thereof, and phosphorus-containingcarboxylic acids, esters, ethers, and amides. The present technology isparticularly useful for formulations in which the total amount ofphosphorus as delivered by various components including the antiwearagent, does not exceed 0.075% or 0.07% or 0.06%. Suitable amounts mayinclude 0.005 to about 0.055 percent by weight or 0.01 to 0.05 percentor 0.02 to 0.05 percent. Non-phosphorus-containing anti-wear agents,which may also be used, include borate esters (including boratedepoxides), dithiocarbamate compounds, molybdenum-containing compounds,and sulfurized olefins.

Other additives that may optionally be used in lubricating oils includepour point depressing agents, extreme pressure agents, and colorstabilizers.

The present technology is particularly useful also when the totalsulfated ash of a lubricant is relatively low, for instance, less than1% or less than 0.8%, e.g., 0.01 to 0.8, or 0.1 to 0.75, or 0.2 to 0.7%.

In a particularly useful embodiment a lubricant formulation may be freeor substantially free of any zinc containing compounds, such as theantiwear agent zinc dialkyldithiophosphate (ZDDP). In other embodiments,the lubricant may be free of or substantially free of any metalthiophosphates.

The lubricant formulations of the present invention are intended toeffectively inhibit siloxane deposit formation and associated enginewear in engines fueled using natural or landfill gas having highconcentrations of silicon, while also maintaining or improving sealsperformance and corrosion inhibition. Thus, in come embodiments of themethod of the present invention, the lubricant composition may comprisegreater than 120 ppm or 125 ppm or 130 ppm or 140 or 160 or 175 or 200or 250 or 300 ppm of silicon. This silicon may be derived fromcontamination from silicon compounds in the fuel source or byproducts ofcombustion of the fuel source.

It is known that some of the materials described above may interact inthe final formulation, so that the components of the final formulationmay be different from those that are initially added. For instance,metal ions (of, e.g., a detergent) can migrate to other acidic oranionic sites of other molecules. The products formed thereby, includingthe products formed upon employing the composition of the presentinvention in its intended use, may not be susceptible of easydescription. Nevertheless, all such modifications and reaction productsare included within the scope of the present technology; the presenttechnology encompasses the composition prepared by admixing thecomponents described above.

EXAMPLES

Reference Example 1 (RE1). A low-ash stationary-gas engine lubricant maybe prepared comprising an oil of lubricating viscosity, 2.54 wt. % of asuccinimide dispersant (chlorine-route); 0.74 wt. % of overbased Casulfonate detergent(s); 0.97 wt. % overbased Ca phenate detergent(s),0.27 wt. % zinc dialkylthiophosphate(s); 2.85 wt. % antioxidants(phenolic, aminic, and/or sulfurized olefin); 0.35 wt. % of a borateester, and 0.007 percent by weight of polydimethylsiloxane antifoamagent (commercial material, about 10% in oil, corresponding to 7 ppmantifoam agent on an active chemical basis).

Preparative Example 1 (PE1). A low-ash stationary-gas engine lubricantmay be prepared comprising an oil of lubricating viscosity, 0.24 wt. %of a phosphite compound(s), 1.8 wt. % of a succinimide dispersant(chlorine-route); 0.6 wt. % of a polyisobutylene succinimide dispersantwith a carbonyl to nitrogen ratio of 4:3, 0.34 wt.% of a boratedsuccinimide dispersant, 0.28 wt. % succinic acid ester dispersant, 0.1wt. % of a polypropylene oxide, 1.2 wt. % of overbased Ca salicylatedetergent; 2.95 wt. % antioxidants (phenolic, aminic, and/or sulfurizedolefin); 0.35 wt. % of a borate ester, 0.01 wt. % of a corrosioninhibitor, 0.05 wt. % of a titanium alkylate and 0.007 percent by weightof polydimethylsiloxane antifoam agent (commercial material, about 10%in oil, corresponding to 7 ppm antifoam agent on an active chemicalbasis).

Each of the documents referred to above is incorporated herein byreference. The mention of any document is not an admission that suchdocument qualifies as prior art or constitutes the general knowledge ofthe skilled person in any jurisdiction. Except in the Examples, or whereotherwise explicitly indicated, all numerical quantities in thisdescription specifying amounts of materials, reaction conditions,molecular weights, number of carbon atoms, and the like, are to beunderstood as modified by the word “about.” It is to be understood thatthe upper and lower amount, range, and ratio limits set forth herein maybe independently combined. Similarly, the ranges and amounts for eachelement of the invention can be used together with ranges or amounts forany of the other elements. As used herein, the expression “consistingessentially of” permits the inclusion of substances that do notmaterially affect the basic and novel characteristics of the compositionunder consideration.

As used herein, the term “substantially free of” means that the materialin question is only present in amounts consistent with contaminationand/or by-products present in commercial grades of desired components.

As used herein, the term “hydrocarbyl substituent” or “hydrocarbylgroup” is used in its ordinary sense, which is well-known to thoseskilled in the art. Specifically, it refers to a group having a carbonatom directly attached to the remainder of the molecule and havingpredominantly hydrocarbon character. Examples of hydrocarbyl groupsinclude hydrocarbon substituents, including aliphatic, alicyclic, andaromatic substituents; substituted hydrocarbon substituents, that is,substituents containing non-hydrocarbon groups which, in the context ofthis invention, do not alter the predominantly hydrocarbon nature of thesubstituent; and hetero substituents, that is, substituents whichsimilarly have a predominantly hydrocarbon character but contain otherthan carbon in a ring or chain. A more detailed definition of the term“hydrocarbyl substituent” or “hydrocarbyl group,” including permissibleamounts of other atoms, is found in paragraphs [0118] to [0119] ofInternational Publication WO2008147704 as well as paragraphs [0137] to[0141] of published application U.S. 2010-0197536.

1. A method for lubricating a natural gas fueled, sump-lubricated,stationary gas engine comprising supplying to the engine a lubricantcomposition comprising: (a) an oil of lubricating viscosity; (b) 0.03 toabout 3.0 weight percent with respect to the lubricant of a phosphitecompound; (c) a metal containing detergent; (d) at least a firstdispersant, wherein the first dispersant is a polyisobutylenesuccinimide dispersant derived from an ethylene polyamine and having acarbonyl to nitrogen ratio equal or greater than 1; (e) at least oneother dispersant selected from the group consisting of a succinimidedispersant having a carbonyl to nitrogen ratio less than 1, a Mannichdispersant, a succinamide dispersant, and a polyisobutylene succinicacid ester dispersant; a boron containing compound in amount to provideat least 25 ppm boron to the lubricant composition; wherein thelubricant composition is free or substantially free of zinc, and whereinthe lubricant composition has a sulfated ash content of less than about1.0 wt. %.
 2. The method of claim 1 wherein the phosphite compoundcomprises a phosphite ester selected from the group consisting ofphosphite diesters, phosphite triesters and mixtures thereof.
 3. Themethod of claim 1 wherein the phosphite compound comprises a phosphitehaving the following formula(R¹O)₃P wherein each le independently is hydrogen or a hydrocarbyl grouphaving 1 to 36 carbon atoms.
 4. The method of claim 1 wherein thephosphite compound comprises a phosphite diester having ester groups of2 to 10 carbon atoms and a phosphite diester having ester groups of 12to 30 carbon atoms.
 5. The method of claim 1, wherein the phosphitecompounds comprises dibutyl phosphite.
 6. The method of claim 1 whereinthe phosphite compound provides 0.001 wt. % to 0.05 wt. % phosphorus tothe lubricant composition.
 7. The method of claim 1, wherein the totalamount of dispersant is 1.0 wt % to 6.0 wt. % of the lubricantcomposition.
 8. The method of claim 1, wherein the first dispersant ispresent in an amount of 0.1 wt % to 2 wt % of the lubricant composition.9. The method of claim 1, wherein the second dispersant comprises asuccinimide dispersant having a carbonyl to nitrogen ratio less than 1.10. The method of claim 1, wherein the metal containing detergent isselected from the group consisting of phenate detergents, sulphonatedetergents, salicylate detergents, salixarate detergents, saligenindetergents and mixtures thereof.
 11. The method of claim 1, wherein themetal containing detergent comprises a salicylate detergent.
 12. Themethod of claim 1, wherein the salicylate detergent has a Total BaseNumber of about 200 to about 700 on an oil free basis.
 13. The method ofclaim 1, wherein the metal of the metal containing detergent is selectedfrom the group consisting of magnesium, and calcium and mixturesthereof.
 14. The method of claim 1, wherein the lubricant compositioncomprises at least a third dispersant, wherein the third dispersant is apolyolefin succinic acid ester dispersant.
 15. The method of claim 1,wherein the lubricant composition has a silicon concentration greaterthan 125 ppm.
 16. The method of claim 1, wherein the engine is fueled bynatural gas having a silicon concentration greater than about 10 mg/m³⁻as measured by gas chromatography mass spectrometry.
 17. The method ofclaim 1, wherein the boron containing compound comprises a borate esterhaving at least one hydrocarbyl group of 8 to 30 carbon atoms.
 18. Themethod of claim 1, wherein the boron containing compound comprises aborated dispersant.
 19. The method of claim 1, wherein the lubricantcomposition has 50 to about 500 ppm phosphorus. 20-21. (canceled)
 22. Alubricant comprising: (a) an oil of lubricating viscosity; (b) 0.03 toabout 3.0 weigh percent with respect to the lubricant composition of aphosphite compound; (c) a metal containing detergent; (d) at least afirst dispersant, wherein the first dispersant is a polyisobutylenesuccinimide dispersant derived from an ethylene polyamine and having acarbonyl to nitrogen ratio equal or greater than 1; (e) at least oneother dispersant selected from the group consisting of a succinimidedispersant having a carbonyl to nitrogen ratio less than 1, a Mannichdispersant, and a polyolefin succinic acid ester dispersant; (f) a boroncontaining compound in amount to provide at least 25 ppm boron to thelubricant composition; wherein the lubricant composition issubstantially free of zinc, wherein the lubricant composition has asulfated ash content of less than about 1.0 percent.